I purchased a 2 (60 watt) light hard-wired wall sconce (230 V 50 HZ AC), but want to convert it to a plug in for future use in a different location (in a nursery now). The sconce has 2 white wires and 2 black wires and an additional copper ground wire attached to the lamp base. I have also purchased a polarized lamp cord, electrical caps and a rotary on off switch. Can this be done??? thanks!

For US 120v fixtures, the two black wires go to the short slot in the outlet and the two white wires go to the long slot.
It'll still work if you switch the black and white wires but there will be less personal safety.

You will have to purchase a three wire cord whip (available at the big box stores) and make your connections inside the fixture. The two black wires in the fixture will attach to the single black wire on your cord and the two white wires in the fixture will attach to the white wire on your cord. the copper wire in the fixture will attach to the green wire on your cord. You will have to provide a means of strain relief so the cord doesn't pull on the wired connections in the "electrical caps". Between the cord and the fixture you will attach interupt the black wire with the in/out of the dimmer switch. The white wire will pass thru the mounting box for the dimmer switch and the green wire will attach to the mounting box (if a metal box) on both the plug side and the fixture side. You might be able to find a cord with a dimmer swith already installed inline.